The assignee of the present invention manufactures and deploys spacecraft for, inter alia, communications and broadcast services, some of which are configured to operate in a geosynchronous earth orbit (GEO). Such spacecraft include a power subsystem including solar arrays and batteries sized to support spacecraft power demands over a mission life (of, for example, fifteen years). A spacecraft in the GEO orbit experiences full sunlight throughout a 24 hour day except for two “eclipse seasons”, one eclipse season centered around the time of the vernal equinox and a second eclipse season centered around the time of the autumnal equinox. During eclipse seasons, which have a duration of about 45 days, a daily eclipse occurs at about midnight local satellite time, the duration of the eclipse being about 1.2 hours or less. The batteries of GEO spacecraft are generally sized to support spacecraft power demands during eclipse periods and, as a result, experience periodic discharges as illustrated in FIG. 1. More particularly, the batteries are conventionally sized such that worst case depth of discharge (resulting from the longest eclipse duration at satellite end of life (EOL)) is not greater than 80%.
Some techniques for operating a battery of a spacecraft configured to operate in GEO (a “GEO spacecraft”) are disclosed in U.S. Pat. Nos. 5,886,499 and 5,939,864, assigned to the assignee of the present invention, and hereby incorporated into the present disclosure in their entireties for all purposes.
For a typical GEO spacecraft having a DC power demand of 15 kW, a battery capacity of 22.5 KW-hrs (15 KW×1.2 hours/0.8) may be required, which implies a very substantial mass and volume overhead cost to the spacecraft design.
Thus, techniques for increasing effective battery capacity without increasing battery size are desirable.